The invention relates to an electrodeless low-pressure discharge lamp having
- a radiation-transmitting discharge vessel which is sealed in a gastight manner and is filled with a metal and a rare gas, which discharge vessel includes a cavity,
- a circuit arrangement for generating a high-frequency current during lamp operation,
- inductive means in the cavity of the discharge vessel during lamp operation and are coupled to the circuit arrangement, the inductive means including a winding of metal wire surrounding a cylindrical core of magnetizable material for generating a high-frequency electric field inside the discharge vessel from the high-frequency current during lamp operation, and
- a cooling body in contact with the cylindrical core for the removal of heat generated in the cylindrical core during lamp operation, the cooling body including a vessel which is closed in a gaslight manner and comprises a condenser, an evaporator, a liquid, and a capillary structure which comprises a winding of gauze surrounding a vapour channel for transporting the liquid from the condenser to the evaporator.
The invention also relates to a cooling body for use in such an electrodeless low-pressure discharge lamp.
Such an electrodeless low-pressure discharge lamp is known from Netherlands Patent 8900406.
The cooling body removes part of the heat generated in the cylindrical core and in the plasma of the electrodeless low-pressure discharge lamp during lamp operation.
As a result, the temperature of the wall of the cavity and the temperature of the cylindrical core remain comparatively low, so that power losses are limited. The heat absorbed by the cooling body is absorbed for the major part by the liquid, which evaporates as a result. This process takes place in the evaporator. The created vapour condenses in the condenser, so that heat is transferred to the condenser. The condensed liquid is then transported to the evaporator, so that there is a continuous circulation of liquid in the cooling body. Especially if the evaporator is arranged above the condenser, the transport from condenser to evaporator takes place mainly through capillary channels in the capillary structure formed from gauze. In addition to the capillary channels in the gauze itself, capillary channels may be formed inter alia between the wall of the gastight vessel of the cooling body and the gauze. If the capillary structure is built up from more than one layer of gauze, capillary channels may also be formed between layers of gauze. It is necessary for the formation of these capillary channels that the gauze lies securely against the wall of the cooling body, and that the various gauze layers lie securely against one another, as applicable. A good contact between the wall of the cooling body and the gauze also promotes the transfer of heat from the evaporator wall to the liquid transported by the capillary structure. In practice, the capillary structure is often obtained in that the gauze is rolled up so as to form a winding, and the gauze winding is inserted into the cooling body. It was found that a good contact between the gauze and the wall of the cooling body, and between the different layers of gauze lying against one another in the cooling body of the known electrodeless low-pressure discharge lamp is often not realised. As a result, the cooling properties of the cooling body are comparatively bad and at the same time poorly reproducible.